1. Field of the Invention
The present invention relates generally to improvements in a tuned cavity, and more particularly pertains to a new and improved cavity tuning assembly wherein provisions are provided for a coarse tune adjustment and a fine tune adjustment of an unthreaded cavity tuning rod.
2. Description of the Prior Art
In the field of tuned resonant frequency cavities such as bandpass filters or notch filters, it has been the general practice to employ a finely threaded tuning rod shaft for changing the tuned frequency of the cavity's resonance. Finely threaded tuning rod shafts, also referred to as cavity plunger threaded rods, are utilized in that usually the adjustments to obtain resonant frequency of the cavity requires very fine tuning so as not to obtain off-resonance reactance of the cavity. Once the resonant frequency of the cavity is reached, the position of the threaded cavity plunger rod is normally not changed depending upon the type of radio service the tuned resonant frequency cavity is utilized in. There are a number of commercially available cavities manufactured which tune from 30 MHz to above 500 MHz in such desirable frequency ranges such as for and by way of example 30 MHz to 50 MHz, 70 MHz to 90 MHz, 110 MHz, to 150 MHz, 150 MHz to 170 MHz, 200 MHz to 400 MHz, 400 MHz, to 450 MHz and 450 MHz to above 500 MHz, etc. These cavities are appropriately characterized as bandpass cavity filters or notch filters. Such finely threaded tuning rod cavity plunger shafts utilized in the above cavities have been unsatisfactory in that it requires numerous turns to change from one resonant frequency to another resonant frequency. The individual consumes valuable time in continuously turning a finely threaded tuning rod cavity plunger shaft in addition to exhausting the muscle strength in the lower arm extremity of the turner's arm and blistering the palm of the hand. Tuned resonant frequency cavities such as bandpass or notch cavity filters are usually intended to be tuned to a single resonant frequency when used with a transmitting/receiving station. When cavities are used by radio technicians to eliminate transmitter interference such as transmitter noise and spurious radiation reduction or receiver intermodulation such as receiver selectivity, it is usually necessary to retune the resonant frequency of the cavities over a wide frequency range. The resulting number of turns of a finely threaded tuning cavity rod plunger shaft consumes valuable time of the technician requiring numerous turns of a small knob plus exhausting of the muscles in one's arm and blistering the hand palm involved in turning the finely threaded tuning rod cavity plunger shaft. The turning of the finely threaded rod in changing frequency can sometimes consume up to five minutes or more in changing from one resonant frequency to another depending on how finely the rod is threaded. If the bandpass cavity filter or notch filter has more than one cavity such as two or three, valuable time is consumed and wasted in rotating the finely threaded tuning rod cavity plunger shaft to the resonant frequency of each cavity. The problem of utilizing a finely threaded tuning rod cavity plunger shaft for a cavity filter is overcome by the present invention of an unthreaded tuning cavity rod plunger shaft wherein provisions are provided for coarse adjustment and fine adjustment of tuning the cavity to a predetermined resonant frequency.